Thanks for using Health Care Magic. Read your query. Yes ,the brown coating can be due to the use of antibiotics . The brown colored coating which you have mentioned suggests overgrowth of bacteria than that is normally present on the tongue. It can be caused by the killing of some bacteria with antibiotics so other bacteria overgrow. I would advice you to brush your tongue gently to remove all food debris and stains along with good oral hygiene maintenance. Avoid smoking if you do smoke and reduce on your caffeinated drinks. Consume high fiber foods. For the sore lip ,apply a topical anesthetic gel. Hope this was useful. Thanks and regards.